Chemical reactions on the surface of metal oxides, such as titanium dioxide and zinc oxide could give a boost for solar cells that convert the sun's energy to electricity.

Chemical reactions on the surface of metal oxides, such as titanium dioxide and zinc oxide could give a boost for solar cells that convert the sun’s energy to electricity.

A previously unappreciated aspect of those reactions could be key in developing more efficient energy systems, said scientists at the University of Washington (UW).

"These refined systems could include solar cells that would produce more electricity from the sun’s rays, or hydrogen fuel cells efficient enough for use in automobiles," said James Mayer, a UW chemistry professor.

“As we think about building a better energy future, we have to develop more efficient ways to convert chemical energy into electrical energy and vice versa,” said Mayer, the corresponding author of a paper about the discovery.

Chemical reactions that change the oxidation state of molecules on the surface of metal oxides historically have been a sole transfer of electrons. New research shows, at least in some reactions, the transfer process includes coupled electrons and protons.

“Research and manufacturing have grown up around models in which electrons moved but not atoms,” Mayer said. “The research looks at a different model for certain kinds of processes, a perspective that could lead to new avenues of investigation. In principle this is a path toward more efficient energy utilization.”

Coupling the transfer of electrons with the transfer of protons could reduce the energy barriers to chemical reactions important in many technologies. For example, using solar energy to make fuels such as hydrogen requires that electrons and protons couple.

The new perspective also could be important for photocatalytic chemical processes, including those designed for wastewater remediation or to create self-cleaning surfaces, such as the outside of buildings in areas with heavy industrial air pollution.

The research focused specifically on nanoparticles, measured in billionths of a meter, of titanium dioxide and zinc oxide. Titanium dioxide is the most common white pigment, used in paints, coatings, plastics, sunscreen and other materials. Zinc oxide also is in pigments, coatings and sunscreens, as well as white athletic tape, and is also in the rubber, concrete and other materials. Nanocrystals closely examine chemical processes at the material’s surface.

Mayer said the goal of the work is to get those working in various technological areas involving metal oxides to think in different ways about how those technologies work and how to make them more efficient.

The work also could prove important in finding more efficient ways to fuel vehicles of the future, he said. Fuel cells transform atmospheric oxygen into water by adding electrons and protons. Coupling those added electrons and protons could make fuel cells more efficient and allow replacement of costly materials such as platinum.

“Chemical fuels are very useful, and they’re not going away,” Mayer said. “But how do we utilize them better in a non-fossil-fuel world?”